Los Angeles Water Quality Report

Last updated: February 2026

LA Water Quality Overview

Los Angeles has some of the most scrutinized tap water in the nation — partly because Californians pay close attention to water (it's scarce and precious in the arid southwest), and partly because LA was the setting for the Erin Brockovich story that brought chromium-6 contamination into public consciousness.

The headline: LA tap water is legally safe — the Los Angeles Department of Water and Power (LADWP) consistently meets all federal and state EPA standards. But "legally safe" doesn't mean "contaminant-free." Independent analysis by the Environmental Working Group has found multiple contaminants in LA water that exceed health-based guidelines, even if they're within legal limits.

Where Does LA Water Come From?

Los Angeles imports the vast majority of its water from hundreds of miles away — the city sits in a near-desert environment that could not sustain its 4 million residents on local rainfall alone. Understanding where the water comes from helps explain the contaminants that end up in it.

1. Los Angeles Aqueduct (Eastern Sierra Nevada)

The original LA Aqueduct, built between 1905 and 1913, brought water 233 miles from the Owens Valley in the Eastern Sierra Nevada. The story of its construction — involving controversial water rights purchases and political maneuvering — was dramatized in the 1974 film Chinatown.

A second aqueduct was completed in 1970. Together, the LA Aqueducts supply about 30–40% of the city's water, primarily when Sierra snowpack is adequate. This source water is generally high quality — cold, clear mountain water. However, it naturally contains some arsenic, uranium, and other minerals from volcanic eastern Sierra geology.

2. Metropolitan Water District (MWD)

The MWD supplies water to 19 million people in Southern California, drawing from two major imported sources:

• Colorado River: Water diverted from the Colorado River at Lake Havasu, pumped west to Southern California via the Colorado River Aqueduct. The Colorado is highly treated but naturally harder (more mineral-rich) than Sierra water.
• State Water Project: Northern California water pumped south through the California Aqueduct. This source passes through the Sacramento-San Joaquin Delta, which can introduce agricultural chemicals and other contaminants.

MWD water typically supplies 50–60% of LA's water, though this varies enormously with drought conditions and snowpack levels.

3. San Fernando Valley Groundwater

LADWP draws a smaller portion of its water from local aquifers in the San Fernando Valley. This groundwater has historically been contaminated by industrial activities — the San Fernando Valley Superfund site dates back to industrial solvents (particularly TCE and PCE) that contaminated groundwater starting in the 1940s and 1950s.

Several groundwater treatment facilities now clean this water before distribution, but the area has also had documented PFAS contamination from industrial and fire-training activities.

The Blend

LADWP blends these three sources continuously, adjusting ratios based on availability, cost, and quality. This means LA water quality can shift seasonally — surface water (aqueduct, MWD) tends to have higher disinfection byproducts, while groundwater can have higher minerals. After the 2020 wildfires, smoke and ash contamination of eastern Sierra watersheds required increased treatment and testing.

Contaminants Detected in LA Water

The following contaminants have been detected in Los Angeles tap water in recent testing. All are within EPA legal limits unless otherwise noted, but comparison with health-based guidelines reveals important nuances.

Disinfection Byproducts (DBPs)

When chlorine (used to disinfect water) reacts with natural organic matter in source water, it creates trihalomethanes (THMs) and haloacetic acids (HAAs). These compounds are found in virtually all chlorinated water systems.

• Total THMs: Average levels in LADWP water have been detected at approximately 60–70 ppb — within the EPA legal limit of 80 ppb, but the EWG health guideline is 0.15 ppb. That's a 400–450x gap between what's legal and what EWG considers safe.
• Haloacetic Acids (HAA5): Average detections around 30–40 ppb, within the 60 ppb legal limit. EWG health guideline is 0.1 ppb.
• Health concern: Long-term exposure to elevated DBPs is associated with increased bladder cancer risk and adverse pregnancy outcomes (particularly miscarriage and low birth weight).

Arsenic

Arsenic in LA water primarily comes from natural geology in the Eastern Sierra source water. Levels are generally low (well below the 10 ppb MCL) but above the EWG health guideline of 0.004 ppb. The San Bernardino County portions of the greater LA water system have historically had higher arsenic levels due to groundwater sources.

Nitrates

Nitrates in LA water come from agricultural runoff (particularly from the Central Valley water imported via the State Water Project) and from local groundwater affected by historical land use. Levels are typically well below the 10 mg/L EPA limit, but nitrates contribute to a cumulative contaminant burden alongside other compounds.

Radiological Contaminants

Small amounts of naturally occurring radioactive materials — primarily radium (Ra-226 and Ra-228) and uranium — have been detected in LA water. These come from the geological formations through which source water passes, particularly Colorado River tributaries. All are within EPA legal limits. EWG flags radium in particular as a concern at levels above their health guideline.

Chromium-6: LA's Most Controversial Contaminant

Chromium-6 — hexavalent chromium — is the contaminant that made Erin Brockovich famous when she documented its presence in drinking water in Hinkley, CA in the 1990s. While Hinkley isn't Los Angeles, chromium-6 has been detected throughout California water systems, including LA.

What Is Chromium-6?

Chromium exists in several chemical forms. Trivalent chromium (chromium-3) is an essential trace mineral. Hexavalent chromium (chromium-6) is a different form — more soluble, more bioavailable, and associated with cancer risk. The EPA's current drinking water standard regulates "total chromium" at 100 ppb but does not have a specific standard for chromium-6.

California's Failed Attempt at Regulation

California was the first state to propose a specific chromium-6 standard — 10 ppb, proposed in 2014. The standard was challenged in court by industry groups who argued the state's cost-benefit analysis was flawed. In 2017, California withdrew the standard under legal pressure.

As of 2026, California has proposed a new chromium-6 standard of 10 ppb. The EWG's health guideline is far stricter at 0.02 ppb — based on the National Toxicology Program's studies linking chromium-6 to gastrointestinal tumors in animal studies.

Chromium-6 in LA Water

Chromium-6 has been detected in LADWP water at levels typically below 10 ppb but above the EWG's 0.02 ppb health guideline. The sources include:

• Natural chromium in the geology of Eastern Sierra source water areas
• Historical industrial use of chromium compounds in the San Fernando Valley
• Regional industrial contamination contributing to groundwater sources

PFAS in the LA Region

PFAS (per- and polyfluoroalkyl substances, "forever chemicals") contamination is a growing concern in the greater LA region, though the contamination is more concentrated in specific areas rather than the entire LADWP system.

San Fernando Valley Groundwater Contamination

The San Fernando Valley groundwater basin has documented PFAS contamination from multiple sources:

• Industrial use: Historical manufacturing operations in the Valley used PFAS compounds in various industrial processes
• Firefighting training: PFAS-containing aqueous film-forming foam (AFFF) used at airports and training facilities contaminated soil and groundwater
• Van Nuys Airport: Airport firefighting activities have been identified as a contamination source for nearby groundwater

LADWP has shut down some groundwater wells in the Valley due to PFAS contamination and treats others with granular activated carbon (GAC) or ion exchange resin. The treated wells are generally within EPA limits.

Broader SoCal PFAS Concerns

Several water agencies in the greater LA metro area have dealt with more significant PFAS contamination:

• City of Burbank: Documented PFAS contamination in wells near the Burbank Airport area
• West Valley Water District (Rialto area): Significant PFAS contamination requiring major infrastructure investment
• Inland Empire communities: Multiple water agencies in San Bernardino and Riverside counties have dealt with PFAS from military and industrial sources

How Drought Affects LA Water Quality

California's chronic drought conditions have real impacts on water quality that many residents don't consider:

Concentration of Contaminants

When water supplies are reduced, water sources often have higher concentrations of dissolved minerals and contaminants. Less water = less dilution. The Colorado River, already one of the most over-allocated rivers in the world, carries higher concentrations of total dissolved solids, nitrates, and other compounds during drought years.

Greater Reliance on Groundwater

Drought forces utilities to pump more groundwater, which may have higher levels of naturally occurring contaminants like arsenic, uranium, and chromium-6. In the San Fernando Valley, more groundwater use means more potential exposure to the legacy contamination in that basin.

Wildfire Ash Contamination

Wildfires have become a regular feature of LA's climate. When fires burn near source water watersheds — including the Eastern Sierra aqueduct system — they can deposit ash and burn byproducts into reservoirs and streams. Some of this material contains benzene, heavy metals, and other toxics from combustion. After major fires, LADWP and MWD conduct additional testing of source water.

Recycled Water Expansion

To address chronic water scarcity, LA has invested heavily in recycled water — treated wastewater that is purified for reuse. The LADWP's "Pure Water LA" program is one of the largest water recycling initiatives in the country. Advanced purified recycled water undergoes microfiltration, reverse osmosis, and UV disinfection, and is generally very high quality — but public perception and the "yuck factor" remain challenges.

LA vs. Other SoCal Water Systems

The greater Los Angeles metro is served by dozens of separate water agencies, each with different source water and treatment. Water quality varies significantly by city and neighborhood:

EWG Data for LA Utilities

The Environmental Working Group has analyzed LADWP water data and identified the following contaminants detected above their health guidelines (though below EPA legal limits):

• Chromium (hexavalent): Detected at levels above EWG guideline of 0.02 ppb
• Bromodichloromethane: A THM; EWG guideline exceedance
• Chloroform: A THM; EWG guideline exceedance
• Dibromochloromethane: A THM; EWG guideline exceedance
• Dichloroacetic acid: An HAA; EWG guideline exceedance
• Trichloroacetic acid: An HAA; EWG guideline exceedance
• Radium-226 and Radium-228: Naturally occurring; EWG guideline exceedance
• Arsenic: Trace levels above EWG health guideline

Note: The key distinction is that all detected levels are within EPA legal limits. EWG guidelines are based on cancer risk models and represent what scientists believe are safe thresholds — often 10x to 1,000x stricter than federal law. Read more about how the EWG database works →

Best Water Filters for Los Angeles

Given LA's specific contaminant profile — particularly chromium-6, disinfection byproducts, and potential PFAS — here's what we recommend:

Whole-House Filtration for LA

For comprehensive whole-home protection — including the water you shower and bathe in — a whole-house filtration system addresses DBP inhalation and skin absorption in the shower:

Frequently Asked Questions